Objectives: 1. To conduct a prospective study of the genetic and environmental factors influencing the individual, family and population dynamics of Australia antigen (Au) and antibody. The population of Graciosa Bay in the Solomon Islands will be tested by immunodiffusion and passive hemagglutination every two years and the results correlated with the census and cultural data. 2. To confirm and extend the observation of excess males among siblings of Au carriers on Santa Cruz in another population with high masculinity (Makira) and in a Melanesian population with a normal sex ratio (the Reef Islands). 3. To compare the distribution of Au in natural and adopted families of Au carriers and non-carriers in an effort to determine the factors contributing to family clustering of Au.